Prestressed connection and fastener therefor

Claim 1

A bolt for forming a controlled radially prestressed connection between a plurality of members formed of material relatively softer than the material of said bolt, said members having aligned bolt-receiving bores defining a right circular surface of revolution, said bolt including a head and having an elongated shank having a nominal conical surface of revolution, said shank having circumferentially spaced arcuate continuously undulating axially extending alternate convex lobes, the crests of which define said conical surface of revolution, and concave grooves, the number of said convex lobes divided by a nominal circumference of the shank portion of said bolt resulting in a number in the range of 14 to 32, a radius of said bolt divided by the radius of said convex lobes resulting in a number within the range of 2 to 5, corresponding portions of the crests and roots of said convex lobes and concave grooves being spaced radially outwardly and inwardly, respectively, substantially the same distance from said conical surface of revolution, said convex lobes effecting a radially outward compression of the material surrounding said bores to prestress said material to a degree sufficient to cause controlled plastic flow of said material circumferentially and radially inwardly into the concave grooves of said bolt to preclude excessive prestress of the material surrounding said bores, the maximum angle of metal flow being tangent to the arc of said convex lobes and concave grooves at the point of transition therebetween.